Solar electric energy has become more practical because solar panel prices have dropped, in some cases to below one dollar per watt. However, end users generally have been unable to fully take advantage of lower solar cell costs because the expense of controlling and manipulating electric power from solar panels dominates the total cost. In particular, control and manipulation circuits can include battery charging/discharging to supply all appliances off grid, conversion of one less desirable solar output voltage to a different voltage such as used in PMMT controllers, conversion of DC solar electricity to AC used by appliances and the like.
Such transformations of solar electric power incur losses every step of the way. Consequently, small scale solar electric site installations generally forgo altogether the use of solar electricity for hot water heating, heat pump activation, clothes dryer, and other high energy use appliances. The solar electric energy field often is associated with a lower energy, minimalist or poor life style suited for depression living, provided to us by the collapse of our fractional reserve banking system.
Another common problem with the big utility, big investment approach to the design and use of local solar electric installations is the high cost of batteries. While not readily appreciated, when included into such systems the batteries are a chemical Achilles heel that wear out and quickly become a most expensive limitation. Consider for example, a $2,000 10 kw hour capacity battery pack system that typically can be charged and discharged 500 to 1000 times. The materials cost of using this chemistry for energy storage in this instance is about 20-40 cents per kilowatt hour, which is at least 2-4 times the cost of grid power in most areas of the US.
Accordingly many discussions of solar electricity begin with the conclusion that the user should abandon a high energy life style to a more “energy efficient” (i.e. give up one or more modern appliances) lifestyle. For example, the notion of using solar electric for hot water heating or for drying clothes is often dismissed as wasteful because passive solar systems must be used since passive solar is so much cheaper and energy efficient. Unfortunately, installations in locations such as northern US or Hokkaido in Japan experience freezing several months a year and seem poor candidates for low cost high efficiency passive roof top water heating.
Finally, as this industry develops, companies develop ever increasingly complicated and expensive hardware to optimize solar panel energy. For example, individual solar panel converters have been developed to improve conversion of solar panel generated electricity but often cost as much or a significant fraction of the panels themselves. A basic challenge is the change in electric solar output characteristics with temperature and irradiation. As light irradiation of the solar panel decreases the available current decreases below an optimum voltage. Also, as temperature increases this optimum panel output voltage decreases. In order to harvest the maximum potential energy, interfacing circuits such as “controllers” have to take into account some or all of these variables. For example, expensive MPPT converters are now chosen for high end systems and can provide more optimum power output (compared to PWM based converters), despite the fact that many of these PMMT converters charge batteries (increase battery deterioration rate) poorly compared to the PWM converters that they replace.
A major challenge has been to optimize solar power output from solar panels despite differing solar irradiation, and more importantly, despite different optimum voltage output at different operating temperatures. FIG. 1 shows, for example that optimum voltage output drops with increasing temperature. MPPT controllers in particular address this problem. However, addition of such complicated circuitry as buck boost converters etc. between the solar panels and a load introduce their own inefficiencies.
For example, a data sheet for a representative converter, the Solar Boost 50 PMMT indicates that although this converter is an excellent system compared to other systems i.e. viewpoint of efficiency, even this high efficiency system wastes on average 3% of solar power under average high lighting conditions and wastes 7% under ⅕ maximum lighting (and presumably more than 10% at lower lighting conditions). These circuit losses are in addition to extra losses incurred by battery charging/discharging, conversion of low voltage DC to higher voltage AC useful for appliances and the like.
A major problem generally is that every circuit conversion or manipulation of solar power wastes some of the available power. As increasingly complicated and multiple added circuits are interposed between the solar panel output and the appliance, this overhead can be very expensive and counterproductive. For example, a modern system design using an MPPT controller might include circuits that convert a solar panel output to a desirable loading voltage (wasting perhaps 1%, 5% or 10% energy within the circuit as mentioned above), which then might charge a battery (wasting perhaps 10% via storage) and then convert the DC into AC (wasting 10% or more). Convertors and invertors sold for solar electric systems generally cite maximum efficiency of the circuits but generally have much lower efficiency for many operating conditions. In many instances a cited “high efficiency” conversion such as a conversion from solar panel to a charger or converter is 95% or more but in actuality often is less than 90% or even much less, depending on actual operating conditions.
In sum, big company developers provide ever more complicated conversion and manipulation systems for enhancing “efficiency.” But these ever complex designs generally are expensive, dominate system cost and add their own inefficiencies under operating conditions that often are overlooked. This field needs less complicated equipment and more efficient matching of solar panel output to appliances.